The
ITU
The International Telecommunication Union is a specialized agency of the United Nations responsible for many matters related to information and communication technologies. It was established on 17 May 1865 as the International Telegraph Unio ...
terrain loss model is a
radio propagation model
Radio propagation is the behavior of radio waves as they travel, or are propagated, from one point to another in vacuum, or into various parts of the atmosphere.
As a form of electromagnetic radiation, like light waves, radio waves are affected ...
that provides a method to predict the
median
In statistics and probability theory, the median is the value separating the higher half from the lower half of a data sample, a population, or a probability distribution. For a data set, it may be thought of as "the middle" value. The basic fe ...
path loss
Path loss, or path attenuation, is the reduction in power density (attenuation) of an electromagnetic wave as it propagates through space. Path loss is a major component in the analysis and design of the link budget of a telecommunication system. ...
for a
telecommunication
Telecommunication is the transmission of information by various types of technologies over wire, radio, optical, or other electromagnetic systems. It has its origin in the desire of humans for communication over a distance greater than that fe ...
link. Developed on the basis of
diffraction
Diffraction is defined as the interference or bending of waves around the corners of an obstacle or through an aperture into the region of geometrical shadow of the obstacle/aperture. The diffracting object or aperture effectively becomes a s ...
theory, this model predicts the path loss as a function of the height of path blockage and the First
Fresnel zone
A Fresnel zone ( ), named after physicist Augustin-Jean Fresnel, is one of a series of confocal prolate ellipsoidal regions of space between and around a transmitter and a receiver. The primary wave will travel in a relative straight line fro ...
for the transmission link.
Applicable to / under conditions
This model is applicable on any terrain.
This model accounts for obstructions in the middle of the telecommunication link, and therefore, is suitable to be used inside cities as well as in open fields.
Coverage
Frequency: Any
Distance: Any
Mathematical formulation
The model is mathematically formulated as:
:
:
:
:
Where,
:
= Additional loss (in excess of free-space loss) due to diffraction (dB)
:
=
Normalized terrain clearance
:
= The height difference (negative in the case that the LOS path is completely obscured) (m)
:
= Height of the
line-of-sight link (m)
:
= Height of the obstruction (m)
:
= Radius of the first Fresnel zone (m)
:
= Distance of obstruction from one terminal (km)
:
= Distance of obstruction from the other terminal (km)
:
= Frequency of transmission (GHz)
:
= Distance from transmitter to receiver (km)
To use the model, one computes the additional loss to each path obstruction (A). These losses are summed and then added to the predicted line of sight path loss which is calculated using
Friis transmission equation
The Friis transmission formula is used in telecommunications engineering, equating the power at the terminals of a receive antenna as the product of power density of the incident wave and the effective aperture of the receiving antenna under i ...
or a similar theoretical or empirical model.
Limitations
This model is considered valid for losses over 15 dB and may be valid for losses as low as 6 dB. In the event that the loss is less than 6 dB or is negative (i.e., gain), this A-value should be discarded.
This model's output is only as good as the data on which it is based and the LOS model it is used to correct.
See also
*
Egli model The Egli model is a terrain model for radio frequency propagation. This model, which was first introduced by John Egli in his 1957 paper, was derived from real-world data on UHF and VHF television transmissions in several large cities. It predicts ...
*
Radio propagation model
Radio propagation is the behavior of radio waves as they travel, or are propagated, from one point to another in vacuum, or into various parts of the atmosphere.
As a form of electromagnetic radiation, like light waves, radio waves are affected ...
*
Longley–Rice model
The Longley–Rice model (LR) is a radio propagation model: a method for predicting the attenuation of radio signals for a telecommunication link in the frequency range of 40 MHz to 100 GHz.John S. Seybold ''Introduction to RF propagation'' John Wi ...
References
{{DEFAULTSORT:Itu Terrain Model
Radio frequency propagation model